Rose Bengal- and Riboflavin-mediated Photodynamic Therapy of Fungal Keratitis Isolates

Abstract

 

Purpose

 

To assess the use of rose bengal (RB) and riboflavin (Ribo) for photodynamic therapy (PDT) to inhibit the growth of fungal isolates that cause infectious keratitis.

 

Methods

 

Three fungi (Fusarium solani, Aspergillus fumigatus, Candida albicans) were isolated from patients with confirmed fungal keratitis and grown on Sabouraud-Dextrose agar plates. Each isolate was suspended in sterile, deionized water and the concentration was adjusted with the photosensitizing agent or sterile water depending on the experimental condition. One milliliter of the isolate suspension was inoculated onto each plate for experimentation. Triplicate test plates were separated into 5 groups: Group 1 - no treatment, Group 2 - 0.1% rose bengal alone, Group 3 - green light irradiation alone, Group 4 - 0.1% riboflavin PDT (Ribo + UVA), and Group 5 - 0.1% rose bengal PDT (RB + green irradiation). Irradiation was performed using either a 518 nm green light emitting diode (LED) array or a 375 nm UVA LED array. A circular area (40 or 60 mm in diameter) was irradiated with a final energy density of 5.4 J/cm ². Plates were later placed in a 30° C non-CO ₂ incubator and observed for growth. Images were taken daily to aid and document the fungi growth for analysis using a Labview program created in the laboratory.

 

Results

 

Rose bengal-mediated PDT was the only treatment that inhibited the growth of the three fungi. At day 3, Group 5 had 95.6% inhibition for Candida albicans, 79.8% inhibition for Aspergillus fumigatus, and 78.2% inhibition for Fusarium solani in the irradiated zones. Riboflavin-mediated PDT had no effect on the growth and the active and passive controls did not either. (Figure)

 

Conclusions

 

Rose bengal-mediated PDT was the only successful growth inhibitor of all three fungal isolates in the irradiated area. Rose bengal-mediated PDT has the potential to be a treatment option for fungal infections. Further experiments must be run to assess the in vivo efficacy and the mechanism of action of the treatment.

 

 

Growth of Candida Albicans for the different treatment groups at Day 3. Groups 1-4 grew with no restriction and Group 5 has a clear inhibition zone in the irradiated area.

 

Keywords: 647 photodynamic therapy • 530 fungal disease • 573 keratitis